Gathering Specimens For Island Fox Tooth Research

In 2019 Friends of the Island Fox supported a research project investigating whether cementum ring structures in teeth could be used to accurately determine island fox age at death. Research Project by Stacy Baker and Juliann Schamel.

Baker and Schamel updated us on their progress mid-March 2020.

"We went up to the Santa Barbara Museum of Natural History last week to collect teeth from the first seven skulls that they are processing for their collection," Schamel wrote in mid-March. An additional five skulls have since been processed.

The researchers explained that the island fox skulls came from Dr. Leslie Woods and the CA Animal Health and Food Safety Lab at UC Davis, which is responsible for conducting necropsies on island foxes when they die on the Channel Islands. These specimens are vital for biologists to understand cause of death, as well as underlying health problems. When an island fox dies, a necropsy (similar to an autopsy for a human) examines organs and tissues in detail to understand the cause of death. Necropsies are vital to identifying disease or any other threat, which might endanger other island foxes. The bodies of these individual animals are stored in special freezers at UC Davis to preserve tissue samples for future scientific investigations, like the tooth project.

During the final stages of the preservation process, cleaned skulls are soaked in cold water for several days. The researchers explain that "At that point in the process, the teeth are very loose and easy to pull out..." A single lower canine tooth was extracted from each skull. Once all of the skulls have been processed, Schamel added, "I think we will be ready to send all the teeth to Matson's Laboratory in Montana!"

See Mike Watling's story for more on how each tooth will be processed.

The plot below shows how fox age estimated by tooth wear does not always match-up with actual island fox age.

We know the actual age of island foxes that are micro-chipped as pups. Biologists performing health checks in the field, however, do not have access to this age information when they are examining individual foxes. They estimate the fox's age by the amount of wear on its teeth. This estimate puts the fox in one of five categories: 

• Age Class 0 - pup to 1 year
• Age Class 1 - young adult
• Age Class 2 - adult
• Age Class 3 - mature adult
• Age Class 4 - senior

The plot above shows data from 1300 exams of island foxes compared with their known ages. The larger the dot the more individuals fell into each category. The more you examine this plot the more you will see. For example: a 4-year-old island fox was almost as likely to be estimated as Age Class 3 as Age Class 2. A few 4-year-olds were estimated as Age Class 1 or Age Class 4. What do you see in the plot for island foxes that are 6 years old? Is tooth wear a reliable way to estimate island fox age? 

This data shows why the cementum research is so important. Island foxes live longer and eat a different diet from the southeastern gray foxes for which the tooth-wear age classes were originally designed.

This project also highlights the broad scientific community involved in researching island foxes. Biologists from Channel Islands National Park are working with the Santa Barbara Natural History Museum, UC Davis, and Matson's Laboratory in Montana, which specializes in cementum age analysis of mammal teeth. Science brings people together.

As this research project moves forward FIF will keep you updated on the findings. Scientific data is vital to making informed conservation decisions that maintain sustainable populations of island foxes.

Friends of the Island Fox invites biologists, ecologists, and other researchers to contribute to our understanding of island foxes. Applications for the FIF Research Grant 2020 are now available.

The island fox cementum analysis research project was made possible through a donation from Safari West.

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